Unmanned aerial vehicles (UAVs) are remotely piloted or self-piloted aircraft that can carry sensors, communications equipment, or other payloads. They have been used in a reconnaissance and intelligence-gathering role for many years. More recently, UAVs have been developed and used for mapping and modeling functions.
Typically, UAVs use a Global Positioning System (GPS) to provide navigation over various terrains. For mapping and modeling, UAVs can be equipped with high resolution cameras, which allow UAVs so-equipped to acquire photos cost efficiently and autonomously from unconventional viewpoints. While UAV technology is advancing rapidly, UAVs are constrained by payload and flight time. To fully exploit UAVs for mapping and modeling, the limited flight-time must be accounted for and an efficient flight path must be utilized.
The challenge of limited UAV flight time is compounded by the requirement of proper photographic coverage to allow proper mapping and modeling. For “easy terrain,” 75% frontal and 50% side overlap photographic coverage is recommended. For “difficult terrain,” 85% frontal with 60% side overlap is recommended. For simple building mapping, oblique photos taken at different altitudes while flying around the building produce acceptable imaging results.
One method for generating solid models of high accuracy suggests that upon determining an initial movement path based on an estimate of a structure to be modeled, images of the structure to be modeled may be captured and surface hypotheses formed for unobserved surfaces based on the captured images. A normal vector and a viewing cone may be computed for each hypothesized surface. A set of desired locations may be determined based on the viewing cones for the entire structure to be modeled and a least impact path for the UAV determined based on the desired locations and desired flight parameters.
While preferred photographic coverage is known and suggested, optimal UAV flight patterns are not. For open terrain a “lawnmower-style” mapping route adjusted for the Earth's contour may be preferred. The lawnmower-style route must be adjusted when the area to be mapped contains “difficult terrain,” manmade objects, vertical obstructions, and/or no-fly zones.